1. Field of the Invention
The invention relates to a thin film magnetic head for use in a magnetic recording apparatus or the like such as a hard disk drive, and a method of manufacturing the same.
2. Description of the Related Art
In recent years, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk drive. A composite thin film magnetic head, which has a laminated structure comprising a reproducing head having a magnetoresistive element (hereinafter referred to as MR element), and a recording head having an inductive magnetic transducer, is widely used as the thin film magnetic head. The MR element has a single-layer or multi-layer magnetoresistive film (hereinafter referred to as MR film) indicating a change in resistance by sensing a signal magnetic field, and based on the change in resistance in the MR film, data is read out. As the MR film, a AMR film indicating Anisotropic Magnetoresistive effect (AMR effect) and a GMR film indicating Giant Magnetoresistive effect (GMR effect) are well known.
In general, many data elements (each of which is an area corresponding to 1 bit of information) are arranged on a track line formed on a magnetic medium, and a space between the data elements is extremely short. Thus, when reading out information of a data element, the MR film of the thin film magnetic head has to avoid being affected by other data elements adjacent to the data element. Therefore, the thin film magnetic head has a structure such that the MR film is sandwiched in between a pair of shield layers of magnetic material having high magnetic permeability. That is, undesired magnetic fluxes (namely, magnetic fluxes from adjacent data elements) mainly flow to the shield layers and do not flow to the MR film, and thereby, an undesired magnetic field is prevented from reaching to the MR film. Such an effect is called a shield effect. A space between the shield layers substantially corresponds to the space between the data elements.
In accordance with a recent increase in the surface recording density of the hard disk or the like, an arrangement density (i.e., a linear density) of the data elements on the track line tends to further increase. Accordingly, it is required that the space between the shield layers of the thin film magnetic head be further reduced. When the space between the shield layers is reduced in such manner, the shield layers and the MR film are arranged closer to one another. However, the shield layers may be affected by a magnetic field generated by the magnetic medium, which leads to random changes in the direction of magnetization. Therefore, there is a problem that when the shield layers and the MR film are arranged close to one another, the MR film is affected by changes in the directions of magnetization of the shield layers, and consequently, output of the thin film magnetic head will become unstable.
In order to solve such a problem, it has been proposed that each of the shield layers is made of a laminate having a ferromagnetic layer and an antiferromagnetic layer, and an exchange coupling between the ferromagnetic layer and the antiferromagnetic layer is used to completely fix the direction of magnetization of the shield layer (Japanese Unexamined Patent Publication No. Hei 9-274712 and U.S. Pat. No. 5,621,592).
However, when the directions of magnetization of shield layers are fixed in such manner, the magnetic permeability of the shield layers is declined, so that it is hard to flow an undesired magnetic flux to the shield layers, which results in a decline in the shield effect. There is a problem that when the shield effect of the shield layer is declined in such manner, the space between shield layers cannot be further reduced, so the thin film magnetic head is incapable of the high-density recording.
The present invention has been achieved in light of the foregoing problems. It is an object of the invention to provide a thin film magnetic head capable of high-density recording and stabilizing output, and a method of manufacturing the same.
A thin film magnetic head of the invention comprises: a functional film having a magnetic transducer function; a first gap film and a second gap film sandwiching the functional film in between, the first and second gap films each having electrical insulating properties; and a first shield layer and a second shield layer sandwiching the functional film with the first and second gap films in between, respectively, so as to prevent an undesired magnetic field from reaching to the functional film, wherein at least one of the first and second shield layers includes an inner layer having a controlled direction of magnetization, a magnetization stabilizing layer controlling the direction of magnetization of the inner layer, and an outer layer having a freely changeable direction of magnetization, laminated in order from the functional film.
In the thin film magnetic head, at least one of the first and second shield layers includes an inner layer having a controlled direction of the magnetization, provided nearest to the functional film. Thereby, in at least one of the first and second shield layers, it is hard to lead a change in magnetization in a region near the functional film. Further, in the outer layer, the direction of magnetization can be freely changed, so an undesired magnetic flux can be fed to the outer layer. Thereby, the shield effect preventing an undesired magnetic field from reaching to the functional film can be fully exerted.
In the thin film magnetic head according to the invention, the thickness of the inner layer is preferably from 10 nm to 300 nm inclusive. Further, the magnetization stabilizing layer preferably contains at least one of an antiferromagnetic material and a hard magnetic material. Moreover, an intermediate layer is preferably provided between the magnetization stabilizing layer and the outer layer. In addition, it is preferable that a thin magnetic head according to the invention further includes magnetic domain control films for applying a bias magnetic field to the functional film, the bias magnetic field controlling a magnetic domain of the functional film, and the direction of magnetization of the inner layer is nearly parallel in the same direction or nearly parallel in a reverse direction, with respect to a direction of the bias magnetic field applied to the functional film by the magnetic domain control films. Further, the functional film may include a nonmagnetic layer; a soft magnetic layer provided on a side of the nonmagnetic layer; a ferromagnetic layer provided on another side of the nonmagnetic layer opposite to the soft magnetic layer; and an antiferromagnetic layer provided on a side of the ferromagnetic layer opposite to nonmagnetic layer. In this case, it is preferable that the antiferromagnetic layer and the ferromagnetic layer are formed to induce an exchange coupling therebetween by a heat treatment at a first temperature, and the magnetization stabilizing layer and the inner layer are formed to to induce an exchange coupling therebetween by a heat treatment at a second temperature different from the first temperature.
Another thin film magnetic head according to the invention comprises: a functional film having a magnetic transducer function; a first insulating film and a second insulating film sandwiching the functional film in between, and a first magnetic layer and a second magnetic layer sandwiching the functional film with the first and second insulating films in between, respectively, wherein at least one of the first and second shield layers includes an inner layer and an outer layer laminated in order from the functional film, and an uniaxially anisotropic magnetic field in the outer layer is closer to 0 than an uniaxially anisotropic magnetic field in the inner layer.
In a method of manufacturing a thin film magnetic head according to the invention, the thin film magnetic head includes a functional film having a magnetic transducer function, a first shield layer and a second shield layer for preventing an undesired magnetic field from reaching to the functional film, and the method comprises the steps of: forming the first shield layer on a base with an insulating layer in between; forming a first gap film having electrical insulating properties on the first shield layer; forming the functional film on the first gap film; forming a second gap film having electrical insulating properties on the functional film; and forming the second shield layer on the second gap film, wherein in the steps of forming the first shield layer and forming the second shield layer, at least one of the first and second shield layers is formed so as to include an inner layer having a controlled direction of magnetization, a magnetization stabilizing layer controlling the direction of magnetization of the inner layer, and an outer layer having a freely changeable direction of magnetization, laminated in order from the functional film.
In a method of manufacturing a thin film magnetic head according to the invention, a thin film magnetic head is manufactured so as to include the first and second shielding layers, at least one of which includes an inner layer having a controlled direction of magnetization, a magnetization stabilizing layer controlling the direction of magnetization of the inner layer, and an outer layer having a freely changeable direction of magnetization, laminated in order from the functional film.
In a method of manufacturing a thin film magnetic head according to the invention, the magnetization stabilizing layer preferably contains at least one of an antiferromagnetic material and a hard magnetic material. Further, it is preferable that the inner layer and the magnetization stabilizing layer are continuously formed through a substantially same means of forming. Moreover, it is preferable that the magnetization stabilizing layer and the outer layer are discontinuously formed through different means of forming.